Ball Motion In Tank Filling CFD Simulation: ANSYS Tutorial

Large industrial containers face violent internal splashing when heavy liquids rush inside. Round sensor floats and safety valves resting on the surface absorb these massive wave impacts. If the fluid pushes a floating object too hard, it can smash into the metal walls and cause severe structural damage. Watching this happen inside a closed steel tank is physically impossible. Relying on basic buoyancy math fails because it ignores the chaotic drag forces.

We use ANSYS Fluent to predict the true trajectory of the floating object on liquid surface when the tank is filling and calculate the hydrodynamic forces acting upon it. This specific CFD project visualizes the heavy liquid, invisible air, and solid body simultaneously. By running this simulation, engineers learn how to evaluate wave impacts and design safer internal sensor mounts. For CFD engineers seeking to solve similar transient moving boundary problems, visiting our professional Dynamic Mesh CFD Simulation library is a helpful step.

Figure 1: The geometric setup showing the initial position of the ball resting calmly on the free surface before filling begins.

Simulation Process: VOF Multiphase and 6DOF Kinematics

We build a 3D industrial container geometry and place a lightweight solid ball inside. The body has a mass of 0.01 kg. It starts by resting quietly on top of the initial waterline. To capture the full physics of this environment, we must solve two distinct mathematical challenges simultaneously. First, we handle the water and air boundary. The tank contains both heavy liquid and light gas. We apply the Volume of Fluid (VOF) multiphase model. This mathematical tool tracks the sharp free surface where the water meets the air. It handles extreme splashing and tracks millions of scattered droplets without failing. If you plan to model other liquid-gas environments, reviewing advanced multiphase CFD simulation projects will clarify these boundary settings.

Second, we set up the solid body motion. Water pumps in from a bottom-right inlet pipe at a continuous speed of 0.5 m/s. We activate the 6DOF solver to calculate the response. It determines how the body should slide and spin. As the object moves, the dynamic mesh automatically stretches and redraws the surrounding computer grid. This creates a highly accurate fluid-structure interaction setup where the fluid and the solid dictate each other’s behavior.

Post-processing: Lateral Wave Drift and Swirling Vorticity Analysis

We evaluate the cause and effect of the fluid forces by analyzing the generated contours and animations. Look at the transient VOF phase animation. At 0.04 s, the red ball floats perfectly still on a flat water surface. Between 0.94 s and 1.1 s, the peaceful environment shatters. The incoming water crashes upward to create violent waves. By 2.04 s, the container becomes 60 % to 70 % full. The object does not rise straight up. It bobs vertically and drifts far left. This proves the trajectory is controlled entirely by the waves, not just basic vertical buoyancy.

Figure 2: The multiphase animation tracking violent bobbing and lateral drift caused by turbulent mixing.

We investigate the velocity map to understand this sideways drift. Water enters the inlet at 0.5 m/s. The internal pressure accelerates this flow into a powerful underwater jet hitting a maximum speed of 1.27 m/s. This red jet shoots completely across the bottom and smashes into the left wall. It pushes the surrounding water upward and to the left. The floating object gets caught in a moderate velocity zone ranging from 0.32 m/s to 0.64 m/s. This specific 0.64 m/s lateral surface current physically drags the 0.01 kg mass away from the center.

Figure 3: The velocity map proving an underwater jet creates a strong surface current that pushes the object sideways.

But why does the object spin? We review the vorticity contours to find the source. Vorticity measures how fast the fluid swirls. Where the fast 1.27 m/s jet rubs against the still water, it creates an intense shear layer. This region spins with a vorticity between 70 s^-1 and 94.98 s^-1. As the surface current flows around the solid ball, the fluid separates. It leaves a turbulent wake directly behind the body with a moderate vorticity of 30 s^-1 to 50 s^-1. This swirling wake pulls the ball backward. Furthermore, the swirling water rubbing against the curved bottom surface applies viscous shear stress. This torque acts like a twisting hand, forcing the object to continuously vibrate and rotate. The mathematical drag force graph confirms these continuous, fluctuating pushing forces acting on the rigid body over the entire physical time.

Figure 4: The vorticity contour mapping the turbulent wake and shear layer that force the body to spin.

Figure 5: The drag force history charting the fluctuating hydrodynamic pushing forces applied over time.

This chaotic fluid-structure interaction places immense mechanical stress on the solid body. The transient drag force graph strictly mathematically captures this unsteady loading profile. Rather than experiencing a smooth, constant force, the object suffers extreme oscillation due to the turbulent wake and crashing waves. The exact physical data shows the rigid body experiencing severe negative drag spikes dropping to exactly -0.011 N, followed immediately by positive force reversals peaking near +0.008 N. For engineering designers, this specific mechanical frequency data is absolutely critical for calculating the material fatigue life of any attached sensor rods or mooring cables.

FAQs About Multiphase 6DOF Tank Filling Training

• What is the function of the VOF multiphase model in this simulation?
• The VOF formulation is mathematically designed to track the precise boundary interface between two immiscible fluids (air and water). It allows the solver to accurately represent surface waves, splashing, and the exact waterline pushing against the floating object.
• What does the 6DOF solver do in this ball motion simulation?
• It calculates the physical forces hitting a solid object. The dynamic mesh then automatically stretches and redraws the computer grid around the object as it moves, keeping the calculation stable.
• Why does the object drift sideways instead of just floating straight up?
• While buoyancy pushes the 0.01 kg mass upward, the powerful 1.27 m/s underwater jet drives a strong lateral surface current. This hydrodynamic drag overpowers vertical buoyancy and pushes the object to the side.
• What does the swirling wake do to the solid sensor?
• The wake behind the object contains swirling water measuring 30 s^-1 to 50 s^-1. This creates viscous shear stress and torque on the curved surface. This force forces the body to constantly rotate and shake.